An estimated 70,000 children and adults worldwide have Cystic Fibrosis (CF). CF is a life-threatening genetic disease caused by mutations in the gene encoding for the CFTR protein. CFTR, cystic fibrosis transmembrane conductance regulator, is a chloride channel that is expressed in multiple epithelial cell types. Mutations in the CFTR gene lead to an abnormal water and electrolytes transport through apical cell membranes of numerous exocrine tissues such as the lungs. Mutations of the CFTR gene have been classified in 5 classes of molecular defects of the protein: Class I, premature termination stop codon leading to complete absence of CFTR protein synthesis; Class II, arrested maturation and intracellular localization defect (processing block); Class III, defective activation and regulation of the chloride transport function (gating defect); Class IV, reduced conductance of the chloride channel; and Class V, reduced CFTR protein synthesis. The most common CFTR mutation is the deletion of the phenylalanine residue in position 508 of the polypeptide chain (mutation F508del, mutant protein F508del-CFTR), which belongs to Class II defect. This mutation is present on at least one allele in about 90% of CF patients, with almost 50% of the genotyped patients being F508del homozygous (Egan et al., Science, 2004, 304:600-602). The F508del mutation causes the failure of CFTR to traffic correctly to the plasma membrane because of protein misfolding that retains the protein in the endoplasmic reticulum. In addition, when the F508del-CFTR protein is correctly localized at the plasma membrane, it also has altered intrinsic chloride channel transport function relative to the wild type (WT) CFTR protein (Dalemans et al, Nature, 1991, 354:526-528).
Until recently, current therapies only treated the symptoms of CF disease, including antibiotics, anti-inflammatory agents, mucolytics, nebulized hypertonic saline, pancreatic enzyme replacement, and lung transplantation (Ashlock and Olson, Annu. Rev. Med. 2011, 62: 107-125; Cuthbert, Br. J. Pharmacol. 2011, 163:173-183). There is thus a great interest in innovative therapies that aim to treat the root causes of CF disease and to correct the underlying basic defects responsible for CFTR loss-of-function.
Since the discovery of mutations in CFTR as the cause of CF, a number of studies have been conducted to find, through standard screening methods, a pharmacological small-molecule approach to correct the dysfunction of the mutated proteins (Becq et al, J Cyst Fibros 10 (Suppl 2), 2011, S129-S145; Rowe and Verkman, Cold Spring Harb Perspect Med. 2013, 3:a009761). For missense mutations, small molecules need to facilitate trafficking and delivery of the abnormal protein to the plasma membrane (correctors) and/or to improve its channel gating (potentiators) (Riordan, Annu Rev Biochem. 2008, 77:701-726). A successful example of potentiator is a VX-770/Ivacaftor, which ameliorates significantly the clinical status of CF patients bearing the G551D mutation and shows no major side effects (Ramsey et al, N Engl J Med. 2011, 365:1663-1672; Yu et al, J Cyst Fibros. 2012, 11:237-245). Some small molecule F508del correctors have also been identified by high throughput screening, the most promising one, VX-809 (Van Goor et al. Proc Natl Acad Sci USA. 2011; 108(46):18843-8) has recently been approved by FDA as Orkambi®, a combination of VX-809 with VX-770/Ivacaftor (FDA approves new treatment for cystic fibrosis, FDA release Jul. 2, 2015). Indeed, because of the limitations in the efficacy of VX-809 as a monotherapy in vitro and in vivo and the effect of VX-770/Ivacaftor on VX-809 treated cells, it is the use of a combination of the two molecules that has been approved.
Compounds and methods for treating CF due to F508del were described in the art. For example, WO 2006/101740 and WO 2006/042949 describe compounds for correcting cellular processing and cell localization of mutant-CFTR.
WO 2012/171954 discloses TMA and structural analogs to correct intracellular localization of the defective F508del-CFTR, and WO 2014/081820 describes compounds of the class of CFTR correctors to correct the misfolding or defective trafficking of F508del-CFTR. However, the mutant protein also show a reduced conductance of the chloride ion. Thus there is also a need to enhance this reduced function.
WO 2004/110352 and WO 2005/120497 describe compounds having activity in increasing ion transport by mutant-CFTR.
Some derivatives of adenine are explored for their activatory properties of CFTR. These compounds are cyclic methylglyoxal diadducts (Boucherle et al, Eur J Med Chem. 2014, 83:455-465).
U.S. Pat. No. 8,362,024 discloses purinyl derivatives for the treatment of diseases associated with the activity of potassium channels.
However, to the Applicant knowledge, the effects of all these molecules tested alone are limited and do not provide significant clinical benefits (Clancy et al Thorax 2012). Moreover, there are controversies about the interest in combining VX-809 with the VX-770 potentiator, as chronic co-administration in clinical studies produced only little evidence for additivity in CF patient homozygotous for the F508del-CFTR mutation (Galietta 2013 Paediatric Drugs 2013, De Boeck K et al. Eur Resp J 2013) and as it has been shown that VX-770 abrogates pharmacological correction of F508del-CFTR by VX-809 (Veit G et al. Sci Transl Med 2014, Cholon D M et al. Sci Transl Med 2014). Moreover, there is no evidence, at the best of our knowledge, that these correctors do interact directly at the site where is located the F508del mutation. Accordingly, there is still a need for compounds that can restore the localization of F508del-CFTR and/or that can activate F508del-CFTR.
By modeling and analyzing comparatively the 3D structure of CFTR (Mornon et al. Cell Mol Life Sci. 2008. 65(16):2594-612; Mornon et al. Cell Mol Life Sci. 2009, 66(21):3469-86; Mornon et al. Cell Mol Life Sci. 2014, Epub ahead of print) and F508del-CFTR proteins, the Applicant found that the amino acid F508 is localized in a structurally important pocket and is an essential key for the opening of the channel. Therefore, the Applicant designed chemical compounds interacting with residues of the pocket, through a novel, structure-based approach. The Applicant found that some of these compounds allow correcting the maturation of the F508del-CFTR protein, thereby restoring CFTR localization and activity.